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Semi-Device-Independent Certification of Causal Nonseparability with Trusted Quantum Inputs
Hippolyte Dourdent1, Alastair A Abbott2,3, Nicolas Brunner3
1Université Grenoble Alpes, CNRS, Grenoble INP, Institut Néel, 38000 Grenoble, France.
Physical Review Letters
|September 9, 2022
Summary
Researchers explored causal nonseparability in quantum theory, finding that even processes unable to violate causal inequalities can create noncausal correlations. This work advances understanding of quantum causality and its certification.
Area of Science:
- Quantum Information Theory
- Foundations of Quantum Mechanics
- Quantum Causality
Background:
- Standard quantum theory assumes a fixed causal structure.
- The process matrix framework allows for relaxing this assumption.
- Causally nonseparable processes challenge the notion of a definite causal order.
Purpose of the Study:
- To explore certification of causal nonseparability in a semi-device-independent scenario.
- To investigate if causally nonseparable processes can generate noncausal correlations without violating causal inequalities.
- To establish conditions for certifying all bipartite causally nonseparable process matrices.
Main Methods:
- Utilizing a semi-device-independent scenario with trusted quantum inputs.
- Defining and analyzing causally nonseparable distributed measurements.
- Imposing natural structure on untrusted operations.
Main Results:
- Certain causally nonseparable processes, including the quantum switch, can generate noncausal correlations.
- These correlations arise even when causal inequalities are not violated.
- All bipartite causally nonseparable process matrices can be certified under specific conditions.
Conclusions:
- Causal nonseparability can manifest as noncausal correlations in specific experimental settings.
- The study provides a method for certifying quantum causal structures beyond traditional causal inequalities.
- This research deepens the understanding of quantum causality and its experimental verification.
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